On bicycles and similar vehicles, the control of the change of speed at the crank gear or at the rear wheel is conventionally effected by means of a cable which is pulled or released by means of a lever or other control member. In its travel, the cable tends to generally follow a tube of the frame. In proximity to the casing of the crank gear, the bare cable changes direction and for this purpose it is guided and directed by means of a cable guide tunnel.
In a manner which is simple, robust and not subject to breakdown, the cable guide tunnels are made of cut sheet steel and suitably formed and they are currently welded to the tube of the frame or to the casing of the crank gear. According to another embodiment, the cable guide tunnel can be solid with collars which can be removably affixed to the tube or casing.
Repeated friction of the steel cable in the metallic tunnel produces premature wear of the cable, its oxidation and jamming. The controls become hard to operate and prove difficult for the cyclist.
When the guide cable tunnel is welded to the frame, these disadvantages can not be avoided by forming a coating, by molding or encasing on the surface of the tunnel a product or material having a low coefficient to friction, since at the time of the welding or brazing this coating will become destroyed.